Method of treating electro-deposited metal



April 1940- c. WHITNEY ET AL 2,196,002

umnon or TREATING ELECTRODEPOSITED mm Filgd June 1:, 1938 v 2Shets-Sheet 1 INVENTOR S Leslie hl fney8 John A. dI-Sh April 2, @940. c.WHITNEY E1 AL METHOD OF TREATING ELECTRODEPOSITED METAL Filed June 15,1938 2 Sheets-Sheet 2 TigJO.

Figll.

mvsmons Leslie C.Whifpey 3 1 John A.Heidlsh Patented Apr. 2, 1940 p aomrco STATES PATENT OFFICE mi lion or man-mo summosrosrrso METAL Leslie0. Whitney, Forest Hills, and John A.

Heidish, Glassport, Pa asalsnors to Copperweld Steel Company, Glassport,Pa a corporation of Pennsylvania Application June 13, 1938, Serial No.213,386

" '2 Claims. (Cl. all-lac) This invention relates to the treatment orelectial in many of the products) the grain structro deposited metal andis herein particularly ture of the copper is unsatisfactory. The copperdescribed as applied to the manufacture of a biwhich is first depositedis flue-g a ned, but as t e metallic wire or rod. Specifically, it islllusthickness of the coating increases, the grains betrated anddescribed as applied to the manufaccome much larger and are'columnar incharacter. 5 5 ture of a bimetallic rod or wire having a steel Becauseof this columnar structure, the opp core and a copper coating, althoughthe inventends to crack if the wire is flexed in any material tion hasnumerous other applications. mount, t us d c destroying the This is acontinuation-in-part of our copendus o es st a d other P ysical p ope tsing application Ser. No. 649,529, filed December For t e fo e fl g M itis commercially 30, 1e32, for Manufacture of electrodeposited desirableto form a bimetallic article of considerlmetal. 4 ably largercrosssectional' dimensions than the A bimetallic wire ha a steel cor anda cop-- final product and, to work this article clown to per sheathcombines high strength with proteche final iz Uufort m t ll'. this pr cr tlon against corrosion and is used in many places e ely e ph sizes a uber of h d t a ove where this combination or properties is desirae de abu e t c s 0f the 0 p- I ble. Suchv/ire also has the property of highelecper p si ed must e consider b y crea or n trical conductivitycompared with ferrous wires. Such a starting y than is t thickness ofthe It has been proposed to make wire of this cllarcopper in, the al prd in Order t0 3 the actor by a wide variety of processes the most d s edt ckn ss of copper there nrand the de-- conspicuously successful ofwhich has been the facts a s o umnar truc re a e emmolterl processwherein molten copper has been vEmil/sited!- poured around a speciallyprepared steel billet, Other d mculties also arise. Processheat-treatthebimetallic ingot thus formed being rolled e s are u nt y sam t ay e anddrawn-into wire. an outstanding advantage necessary, for mp o eal e ateal of such process is that a permanent union be- Whi n M 5 1 Order to pm f further tween the copper and the steel is formed, but it wiredrawing, or it may be desirable to anneal, also has certaindisadvantages, among them benormalize, or oth w se 11 t e the l P 'ingthe fact that it is impossible by the use of n t i order o d e p t e i ep y ical cr pmolten copper to produce a sheath of as great erties-During such heal m n is e r purity and high electrical conductivity asis other porous Zones a likely to mil/e109, l u- 8G desired. It is alsodlmcult, particularly where la ly w th a thick oa- These l st s a e thepercentage of copper in the wire is high, to probably due to thepresence of foreign matter obtain concentriclty of the core and thesheath. which expands or forms a s up n h at n o H These cllmcultles.which are inherent in the they may e due to interruption in e c ystalolder processes, argue for the manufacture of gr wth nd consequent linesof weakness in the bimetallic wire by a process of. electrodeposltl'ngmetal. Howeve We do not limit ourselves to the copper over a steel core,but while many ateither 0! these theories. The fact remains that temptshave been made most of them have reblisters and p r s Zones aremanifested l on sulted in failure because of a number of dif-- heatingof athick Goemlally Produced l ctrorficulties which arise out oz? thestep of electrodeposited body of metal, especially where the wdepositing a relatively thicls coating of the .copsame has been put onin successive layers, as, for per or other sheath metal. example, bypassing it through a series of cost- It hasbeeln propwed to draw thesteel wire to lug baths. Once the blisters or porous zones have i itsfinal slze ;and deposit the copper thereov'er. developed subsequentdrawing of the wire in the 45 This, however} is not satisfactory for anumber ordinary fashion does not heal them and a de-' of reasons. Itisdesirable to subject the blmetal tective product results. lic body tocold work in order to develop the Considerable culty also arises due tolacll: proper physical properties. The copper in the of proper adherenceof the copper to the base "as deposited" condition is porous. it isdlflicult metal. Even when the greatest care is elmaloyed, 50

if not impossible to obtain merely by electro difflculties arise on thisscore. Attempts to draw deposition a continuously extending and por wiremade in this fashion, particularly where manent bond between the copperand the base blisters or porous zones have developed, result in metal.It the copper deposit is of any substan flaking or peeling of the copperand consequent M tlal thickness (and such thicknesses are essendamagecrspoilage oi the wire. 5@

Attempts have been made to overcome these defects by heat treatment, butthese have not proved satisfactory. A thin coating of copper may by heattreatment be made to adhere fairly well to the base metal, but thedifficulties of porosity are still present.

The difliculty of blistering upon heating has been recognized and it hasbeen attempted to overcome the same by careful control of the heatingconditions. However, such proposals have not worked out satisfactorilyin practice. If it is attempted to limit the heating of the metal tosuch low temperature that the blisters do not develop, it is frequentlyimpossible to obtain the desired results, and such operation requires somuch time as to render it commercially impractical. Furthermore, suchprolonged heating is conducive to the growth of very large grains, whichgrain structure is frequently undesirable.

We have found that these difficulties may be overcome and a superiorproduct obtained by going contrary to established practice anddeliberately heating the metal, and in some cases in an amountsufficient to develop porosity, and then working it under suchconditions as to compact and homogenize the porous metal. We prefer tocarry out these steps on the electrodeposited metal preliminary to anyfurther reduction thereof and have discovered that by so doing the metalis put in such condition that it can be readily worked and can besubsequently heat treated without any danger of blisters or other porouszones developing. We have found that there are certain limitations as tothe temperature to which the electrodeposited metal is heated and theextent of the hot drawing to which it is subjected. Specifically, thedeposited metal must be heated to a temperature of about 1000 F. orhigher and subjected to a reduction in sectional area by hot drawing ofat least 5%.

We prefer to carry out the steps of our process in a continuous manner,preferably passing the metal continuously through a heating zone and hotworking it as it is delivered from such zone.

We have found that it is important to maintain the metal during theheating and hot working steps in an atmosphere which inhibits theformation of undesirable compounds of the electrodeposited metal. It isdefinitely undesirable, for example, to allow the formation of oxides ofthe metal. If the metal is blistered or cracked, the formation of oxidesopposes the healing of the surfaces during the hot work which followsthe development of such porous zone. We have successfully employed anatmosphere of hydrogen.

The use of our process gives as a new and improved product a metal bodycharacterized by the purity of electrolytic metal and a grain structureof the character of annealed wrought metal. Stated in another way, themetal has the purity of electrolytic metal and it' has been homogenizedby heat and pressure. Such metal is particularly desirable as a sheathfor a bimetallic article.

In the accompanying drawings, illustrating our invention as applied tothe manufacture of bimetallic wire with a steel core and a coppersheath:

Figure 1 isv a side elevation of a bimetallic wire broken away to showthe successive layers;

Figure 2 is a side elevation of a wire which has been heated to suchtemperature as to develop blisters;

Figure 3 is a transverse section of the blistered wire shown in Figure2;

Figure 4 is a diagrammatic view illustrating one form of apparatus bywhich our process may be carried out;

Figures 5 and 6 are diagrammatic views illustrating further steps in themanufacture;

Figure 7 is a view similar to Figure 4 showing the preferred practice ofthe invention and,

diagrammatically, the apparatus used therein;

Figure 8 is a partial sectional view taken along the plane of lineVIII-VIII of Figure 7;

Figure 9 is a photomicrograph showing the structure of the copper asdeposited;

Figure 10 is a photomicrograph showing the electrodeposited copper afterheating only; and

Figure 11 is a photomicrograph showing the electrodeposited copper afterheating and hotworking. a

The bimetallic wire shown in Figure 1 comprises a core 2 of drawn steel.We have successfully employed simple steel wire .375" in diameter. Thecarbon content is immaterial and will' be determined by the physicalproperties desired. It will be obvious, of course, that alloy steelwires may also be employed if need be. The core 2 is covered with acontinuous sheath 3 of acid copper. The copper may be deposited directlyon the steel, but we have found it advantageous to use an intermediatelayer 4 of nickel. It will be understood, of course, that instead ofnickel, alkaline copper, electrolytic tin, zinc or iron, or other metalmay be used, or if desired, the wire, prior to the deposition of copper,may be subiected to a chemical dip of arsenic trioxide in hydrochloricacid and water.

The percentage of copper in the final product will vary according to therequirements of the user. Bimetallic wire is usually rated according tothe percentage relation which its conductivity bears to a solid copperwire of the same diameter. Thus a conductivity wire" is one whose ratioof steel to copper is such that the wire will have a conductivity 30% ofthe conductivity of a solid copper wire of the same diameter. In orderto make 30% conductivity wire from a bimetallic starting body having asteel core .375" in diameter, it is necessary to electrodepositsufficient copper to make the diameter of the starting body 0%conductivity wire may be made from a starting body having a steel core.375" in diameter and a diameter, with the copper sheath, of .467". Theabove examples require copper deposits of .028" and .046", respectively.These deposits are very much heavier than those employed in commercialelectroplating and introduce the difficulties above referred .to. Theordinary commercial electrodeposit for purposes of surface protection ismeasurable only in ten-thousandths of an inch, whereas we are concernedwith electrodeposits very much thicker. For example, even a wire havinga copper sheath whose cross section is of the total cross section of thewire willhave a thickness of .005" on a core .375". These heavydeposits, when heated to the temperatures required for heat treating themetal, are very likely to develop blisters. We have shown blisters at 5in Figure 2.

Figure 3, which shows the wire in cross section, illustrates a blister5a within the boundaries of the copper and a blister 5b at the interfacebetween the copper and the steel. The blisters when developed are likelyto lead to veryserious difiiculties either in subsequent manufacturing 1trolled laboratory conditions to obtain a deposit wherein a minimum ofblisters and porous zones will develop upon heat treatment, we are ofthe belief that it is difllcult it not impossible to avoid them entirelyand have ioundthat they are of frequent occurrence in commerciallydeposited copper. Figure 9 is a photomicrograph of a commercial depositmagnified to 90 diameters, showing an etched section of a test specimenwith the steel core below a layer of cyanide copper and a main depositof acid copper above. It will be noted that, asv viewed acid coppershows distinct lines of interruption, as indicated at 6 in the drawings.This particular sample was formed by'a succession of deposits, thearticle passing through a series of electrolytic baths. The columnarstructure, indicated at 7, is very marked in the drawings and ischaracteristic of heavy deposits. The grain boundary lines extend in adirection generally perpendicular to the axis of the wire and form linesof weakness which may cause cracking of the copper on flexing or bendingof the wire, or an attempted reduction thereof as by drawing. A radialcrack appears at la, and is found to extend a consider-= able distancealong the length of the'test specimen.

The deposited copper may be recrystallized by heat treatment. Forexample, Figure 10 shows an etched section of avspecimen'cut from thesame piece and adjacent the same point in the piece as that illustratedin Figure it, after being heated in a reducing atmosphere to 1400 F. for30 minutes and allowed to cool man. It will be noted that the copper hasrecrystallized into very large grains. Such grains may beobjectionablein certain cases and the heating time is commerciallyexcessive. The radial crack has been enlarged.

It is desired to obtain a structure which is free or excessively largegrains and radial cracks and yet reduces the heating time to a minimum.We effect this result and homogenize the copper by combined heating andworking. I

Figure 4 illustrates diagrammatically one form of apparatus which wehave successfully employed for this purpose. wire W havinga wroughtsteel core and an electrodeposited sheath and of the dimensions givenabove is fed from a coil a through a water seal Q to a hollow heatingtube iii. The tube is contained largely within a furnace ii heated inany desired manner, as by burners it. The tube iii is kept filled withhydrogen supplied from a source H through a reducing valve l3 and a tube16 communicating with the pipe in. In the passage of the wire W throughthe pipe iii, it is raised to the desired temperature and is then incondition to be subjected to hot work. This is accomplished in theexample shown by a wire die IS. The delivery end of the pipe illprojects beyond the end of the furnace H and is tapered as indicated atE6. The delivery end of the pipe I0 is very close to the die l5 andwithin the die holder l7.

under the microscope, the.

In Figure 4, a bimetallic The small space between the die l6 and theopen end of the pipe I6 is packed by.

the drawing lubricant, as indicated at Ii. The lubricant employed isgraphite mixed with grease, which is a reducing compoundand it is placedaround the end of the tube so as to seal. it of! from the atmosphere aswell as to provide lubri cation for drawing. The wire is drawn throughthe apparatus by a drawing block IQ of usual construction. The highlydesirable final structure obtainable by our process is shown in Figurell, which is l a photomicrograph of an etched section oi a specimen cutfrom the same piece and from the same location therein as thatillustrated in Figures 9 and 10. After heating, as before described,this specimen was given a 9% reduction by hot drawing through die it andcooled under a water spray. It will'be noted that the copper has beenhomogenized by heat and pressure so as to give a grain structure of thecharacter of annealed wrought metal. At'the same time, ithas the purity01' electrolytic metal and is free of porosity. The heating to which thewire was subjected wassufiiclent to cause blisters and porous zones, buttests of the metal show it to be free of these defects. The radial crack1a which originally ex.- tended through the several specimens, has beenfully closed.

It will be further noted that the structure illustrated-in Figure 11 isnot of the columnar form which characterizes the deposited copper shownin Figure 9. The grains are smaller than in Figure 10, more uniform insize, and definitely equiraxed. Another important advantage is that avery flrm union between the steel and thecopper is eflected. This unionis so perfect that it successfully resists the severe tests hereinafterdescribed.

The product shown in Figure ii may be subsequently worked either hot orcold and heat treated without danger of developing blisters or porouszones. In Figures 5 and 6, we have diagrammatically illustrated suchfurther treatment. The wire W1 is shown in Figure 5 as being cold workedby drawing through a die it! and thereafter passed through a heattreating furnace 2i,as shown in Figure 6. This subse=- quent coldworking and heating further im= proves the product.

Figures 7 and 8 illustrate a modified form of apparatus which we. nowprefer for practicing the method of our invention. As therein shown, awire W similar to that indicated in Figure 4 is unwound from a reel ttonto a guide sheave 3i. From the sheave 36, the wire passes over acoating sheave 82, partially immersed in a bath of die lubricant 33,composed of engine oil and graphite. As shown in Figure 8, the sheave $2has a large peripheral groove 3% divided into segments by notched,radial vanes 36. The lat- Sid ter insure the picking up of suficient dielubricant to thoroughly coat the wire.

From the coating bath 3%, the wire passes through a muille 38, a die31', mountedon a support 38, and a cooling tank 39 provided with watersprays 40, after which it is wound up on the usual drawing block ii. Thewater sprays quickly cool the material to room temperature and 'make itpossible to operate at drawing speeds higher than'would otherwise bepossible.

Electrical connections 42 and 43 extend i'roma suitable source ofheating current to the sheave 3| and support 38, respectively. By meansof these connections, electric current is passed through that portion ofthe wire betweenthe sheave II and support 38 to heat it to the desiredtemperature, say 1400 F. By making conaffects the change in grainstructure already referred to, but also causes the die lubricant to bebaked onto the wire. This heating also creates a reducing atmospherewithin the muflie.

Test specimens of material produced according to the procedure justdescribed may be conveniently made up as follows:

To provide specimens having different conductivity precentages (viz.,40%, and 20%), short lengths of steel rods having diameters of .500",.535, and .585" are subjected to electrodeposition suilicient to buildthem up to a common diameter of .650". For greater accuracy, thesespecimens are then turned down to a slightly smaller diameter such as.632", and then etched in nitric acid to a final diameter of .630". Thetest rods are then subjected to heating, for example, to 1000 F., for aperiod of 30 minutes in a reducing atmosphere. After heating, the rodsare hot drawn through. dies which would normally produce variouspercentages of reduction in sectional area, e. g., 5%, 15%, 25%, and Thepull required to draw the material through these dies, however, resultsin drafts of approximately 10%, 19%, 28%, and 38%.

After heating and hot drawing, a short length is cut out of the midportion of the rods and the steel'core drilled through from end to end.The drilled sections are then placed in a hot 10% sulphuric acid bath todissolve out the remainder of the steel core, leaving the copper in theform of a tube.

While we prefer to heat the material to 1000 F. or higher, to insureremoval of all defects, it is possible to obtain an improvement of thephysical properties of the deposited metal by heating to a somewhatlower temperature. Tensile tests on tubular specimens indicate that themaximum increase in ductility may be obtained .by heating to thetemperatures indicated belowfif the electrodeposition has been carriedout under optimum or ideal conditions:

Percent conductivity Percent hot of specimen Tempemmm' o reduction 20600to800orthe practice l8 10001101200 10 to is 30 800 to 1000 or thepractice. 10 to 38 1N0 10 to 28 40 800m 1000 l0t0 18 If theelectrodeposition has been carried out under somewhat less favorableconditions, such as prevail in ordinary commercial practice, it has beenfound that a higher temperature say from 1400 F. to 1600 F. will producethe maximum improvement in physical properties of 30% conductivitymaterial with a hot reduction of 10%.

Tubular specimens 1" long may readily be test-- ed for ductility andlocal defects; such. as the radial crack Ia shown in Figures 9 and 10,by driving a conical plug into one end, forcing the ends to "hell ou Thespecimens which have been subjected to heating only, without hotdrawing, and those heated only to 1000 F. or below, regardless of theamount of hot reduction (up to a maximum of 29%) show definite localfailure as by cracking or splitting axially. Specimens which have beenheated to temperatures above 1000 F. (up to a maximum of 1800 F.) andhot drawn to reduce them by from 9% to 29%, all show uniform bellingout" with corresponding thinning of the edges, but without any localizedfailures such as cracks or longitudinal splitting. This confirms theconclusions drawn from Figures 9, l0, and 11 as to the healing ofdefects such as radial cracks in the copper sheath by the combinedheating and hot drawing.

Our investigations show that the temperature to which the copper-steelbody above described should be heated in carrying out our process isbetween 600 F. and 1900 F. As the maximum temperature is approached,care must be exercized to make sure that the copper does not flow andbecome eccentric to the steel. If it is attempted to operate below theminimum temperature above given, it will be found difficult orimpossible to carry out the processsuccessfully. It is preferred to usea temperature at least as high as that of any subsequent treatment towhich the copper-steel body may be subjected and to follow this with thehot working at any temperature within the limits described above.

The reduction effected by the die l5 should be sufficient to insure thatits influence is felt throughout the copper. This is best insured byproviding a sufficient reduction by the die to reduce the crosssectional area of the base as well as to work the copper. .Generallyspeaking, the thicker the copper, the more mechanical work should bedone in order to insure satisfactory results.

We have herein described our invention with particular reference to abimetallic wire having a steel core and a copper sheath. However, theinvention is of general applicability and may be used in the manufactureof bimetallic bodies of other forms, such as rods, sheets, strips, andshapes. It may also be used for the manufacture of bimetallic ormultimetallic bodies other than copper on steel, as for example, nickelon copper, nickel on iron, chromium on copper, copper on nickel, etc.The invention is also useful in the manufacture of bodies of a singlemetal, as for example, copper may be deposited on a copper core, or theinvention in certain aspects may be used for rendering workablecommercial cathode copper which heretofore has been consideredmechanically unworkable. It will be understood, therefore, that while wehave illustrated and described a present preferred embodiment of theinvention, in addition to an alternate practice, it is not so limited,but may be otherwise embodied or practiced within the scope of thefollowing claims.

We claim:

1. In the method of making a bimetallic body, the steps consisting inelectrodepositing a thick layer of copper over a steel base, heating thebody and hot drawing it under non-oxidizing conditions which inhibit theformation of undesirable compounds of the electrodeposited metal toreduce the bimetallic body by a single pass through a die to a thicknessapproximating the original thickness of the base, thereby to compact andhomogenize the copper.

2. In the method of making a bimetallic body, the steps consisting inelectrodepositing a thick layer of copper over a steel base and hotdrawing the bimetallic body under non-oxidizing conditions which inhibitthe formation of undesirable compounds of the electrodeposited metal toreduce it by a single pass through a die to a thickness substantiallyequivalent to that of a bimetallic body formed from a base of the sameoriginal thickness as the base of the body in question, and

having a coating of copper of such thickness that includingelectrolytically depositing the sheath 2. firm bond between the steeland the copper can on the core to a thickness such'that the sectional besecured by heating alone; area of the sheath is a substantial fraction(e. g.

3. In the method of making electrodeposited about one-tenth or greater)of the sectional area copper, the steps consisting in electrodepositinga of the core and altering the grain structure of the 6 layer of copper,heating the metal, drawing the sheath as deposited to render the articlecapable metal while hot through a die, and lubricating of beingdrastically cold worked, by heating the the metal during drawing by areducing subarticle to a temperature suitable for hot working stance.and reducing the sectional area of the article at 4. In the method ofmaking a bimetallic wire, least 5% by drawing while at substantiallysuch 10 the steps consisting in electrodepositing copper temperature. onan elongated steel core such as a rod or wire, 7. In a method of makingbimetallic wire comheating the bimetallic body and drawing the bip singa ferrous core and a opp r shea h. the metallic body while hot through adie, and lubristeps including electrolytically depositing copper eatingthe body during drawing by a reducing on a ferrous core to a thicknesssuch that the secsubstance. tional area of the copper is a substantialfraction 5. In the method of making a bimetallic wire, or that of thecore, and altering the grain structhe steps consisting inelectrodepositing a suiture of the copper as deposited to render thewire ficiently thick layer of copper on an elongate steel capable ofbeing drastically cold drawn by heatcore such as a large wire or rod asto produce ing the wire to a temperature suitable for hot 29 a conductorof about 30% conductivity, heating working and reducing its sectionalarea at least the bimetallic body and reducing it while hot by 5% bydrawing while substantially at said temfrom 5% to about by a single passunder perature. non-oxidizing conditions through a die. LESLIE C.

6. In a method of making a composite metallic JOHN A. HEIDISH. 25

article including a core and asheath, the steps

